The present invention relates to a method and a device for supplying at least a first fluid to a combustion chamber in a heat-generating plant, e.g. a heating boiler or a kiln. More specifically, the present invention relates to a method and a device for controlling the emissions from such a combustion chamber.
Today a significant part of the energy generated in the modern society comes from burning of fuel. This includes wood fuels, straw, waste such as industrial, municipal, hazardous and hospital waste and also hard coal, lignite, peat, lime sludge and black liquor. These fuels are burnt in heat-generating plants in combustion chambers and results in unavoidable emission of more or less hazardous substances.
To reduce the amount of emission different devices has been contemplated and successfully implemented in existing plants, as well as in new. In this respect reference is made to SE9201747-4, SE9304038-4, SE9802570-3 and SE0000103-2 all in the name of ECOMB AB and included herein by reference.
According to the references above reduction of emissions can be achieved by introducing secondary air into the combustion chamber in a heat-generating plant.
Another way to achieve reduction of emission is to introduce substances, such as NH3, to reduce specific emissions, such as NO and NO2, commonly denoted NOx. The ammonia reacts with the NO and the NO2 to form substances which is not harmful to the environment.
One problem with introducing another harmful substance, such as ammonia, is that slip can occur, i.e. ammonia is emitted to the environment.
Another problem is that the reaction between ammonia and NOx may not always be optimal resulting in increased cost, when excessive amounts of ammonia is used to reduce the emission of NOx, but with limited success.
Yet another problem, realized by the inventor, is that the temperature of the combustion chamber, where NH3 is introduced, is not optimal for reaction with NOx.
It is a main object of the present invention to provide an apparatus and method for controlling the temperature in a combustion chamber to be within a preferred range, within which range a first fluid is particular active to reduce the emission of at least a first substance.
It is in this respect a particular object of the invention to provide such apparatus and method for reducing the emission of NO and NO2.
It is still a further object of the invention to provide such apparatus and method for effective use of supplied ammonia for reduction of emission of NO and NO2 so that no or minimal slip of ammonia emission occur.
These objects among others are, according to a first aspect of the present invention, attained by providing a method for reducing the emissions from a combustion or gasification plant having a combustion chamber. The combustion chamber is housing means for insertion of a first fluid into said chamber, where the introduction of said fluid into said chamber is effective to reduce the emission of at least one substance. Said fluid having an optimal operating temperature range for which said fluid is particular active and thus emission is particular low. The method comprises the steps of establishing the temperature in a volume where said fluid is introduced into said combustion chamber. If the temperature is higher than said optimal operating range a second fluid is introduced into said chamber, where said second fluid is effective to reduce the temperature in said volume. If the temperature, on the other hand, is lower than said optimal operating temperature range a third fluid is introduced into said combustion chamber. Said third fluid is effective to increase the temperature of said volume.
In more detail, the method according to a preferred embodiment of the present invention comprises an axially displaceable tube, which can be introduced and withdrawn from said combustion. Chamber said tube is used for introducing a fourth fluid, e.g. air or re-circulated flue gas, into said chamber. The fourth fluid is inserted under pressure to create swirls or turbulence in the flue gas flow to change the flow pattern and improve mixing in the combustion chamber. Through said tube said first and second or third fluid is introduced into said chamber. Alternatively, is it also possible to use said tube for insertion of only one or two of the three fluids, and using a separate means for introduction of the remaining fluids.
A thermocouple is arranged on said tube for measuring the surrounding temperature where said first fluid is introduced into said chamber. Alternatively, said thermocouple may also be arranged on the wall of the combustion chamber. Thus it is possible to continuously measure the temperature and dynamically control the introduction of said fluids into the combustion chamber to regulate the temperature.
According to another preferred embodiment 25% ammonia aqua is mixed with water and injected into the combustion chamber through said tube. The water in the mix serves to reduce the temperature in the chamber.
The amount of water injected into the chamber is controlled to reach said optimal operating temperature range. The proportions between the ammonia aqua and the water is also controlled, in dependence of the amount of water injected, so that an optimal amount of ammonia is introduced into the chamber so as to reach a maximum reduction of the emission of NO and NO2 and also to minimize the ammonia slip. The amount of water and ammonia to be introduced into the combustion chamber varies with, for instance, the size of the combustion chamber and the temperature.
These objects among others are, according to a second aspect of the present invention, attained by providing a device for reducing the emission from a combustion or gasification plant having a combustion chamber. A supplier is arranged in said chamber for supplying at least a first fluid. The fluid is effective to reduce the emission of at least one substance and has an optimal operating temperature range. The device also comprises means for controlling the temperature in at least a volume of said chamber to be in said optimal temperature range.
According to a first preferred embodiment of the second aspect of the invention, said device comprises an axially displaceable tube for displaceable insertion into said chamber. The tube is sealed in a first end and comprises orifices along its length. The first end is inserted into said chamber. Compressed air is supplied in the second end of said tube and forced to exit the tube through said orifices creating swirls in the flue gas in the combustion chamber, water is fed through a hose to the tube and thus made to eject, by the compressed air, through the orifices and into the combustion chamber. Ammonia aqua is mixed into said water in proportions suitable to achieve minimal or at least reduced emission of NO and NO2. The device further comprises a thermocouple, preferably arranged on said tube, coupled to control means. Said control means is arranged to increase the amount of water ejected into the chamber if the temperature is above the optimal operating range and also to control the proportion of ammonia aqua mixed into the water so that an optimal amount of ammonia is introduced into the combustion chamber.
The device further comprises means for injecting a third fluid into said combustion chamber. The third fluid is effective to raise the temperature if the temperature is below the optimal operating temperature range. Suitably the third fluid is inserted into the chamber through the tube, but separate means is also possible to use. The third fluid can be hydrocarbon fuel in gaseous, liquid or fixed form such as natural gas, oil or pulverized wood, which will increase the combustion if introduced into a combustion chamber.
Preferably, the water is drawn from the mains, or is wastewater or is water that has been used for cooling the tubes.
If the object is to reduce the emission of NO and NO2, a suitable operating temperature range is 800xc2x0-1200xc2x0 C., preferably 830xc2x0-1000xc2x0 C. and particularly 850xc2x0-950xc2x0 C.
Further characteristics of the invention and advantages thereof will be evident from the following detailed description of embodiments of the invention.